The present invention relates generally to semiconductor manufacturing process systems, e.g., ion implantation and wet bench systems, and more specifically to apparatus and methods for utilizing exhaust gas for recirculation in such systems, in a manner substantially reducing the effluent burden on the exhaust treatment system and infrastructure of the semiconductor process facility.
In the field of semiconductor manufacturing, a variety of unit operations in the semiconductor plant are exhausted at a high volumetric rate due to the hazardous or toxic character or the chemicals contained or processed therein. In general a house blower is mounted exteriorly, typically on the roof, which pulls air through the interior space of the tool to contain any hazardous materials released in the process zone by leaks in the process piping. This large volume of air is intended to capture and sweep contaminates away and minimize the risk to personnel. This sweep air is typically vented to the atmosphere after passing through some type of final scrubber system.
In the semiconductor manufacturing plant, a number of processes may be conducted in enclosed chambers and generate hazardous xe2x80x9cprocess effluentxe2x80x9d streams composed of un-reacted starting materials and by-products which require treatment to abate the deleterious components therein, so that the purified effluent can be discharged to the atmosphere.
Accordingly, the typical semiconductor processing facility produces process exhaust that is characteristically contaminated with feed and product/byproduct contaminants, as well as sweep exhausts that typically have only a low level of contaminants therein.
It has been common practice in the semiconductor industry to subject semiconductor xe2x80x9cprocess effluentsxe2x80x9d to a wide variety of treatments, including point of use combustion and incineration, wet and dry scrubbing, liquid-liquid extraction, chemical complexation, distillative purification, cryoplating of contaminants, etc.
With regard to specific effluent-producing processes, the semiconductor manufacturing unit operation of ion implantation is particularly problematic in respect of producing high volume, low contaminant effluents. Such effluents are large in volume, and the species requiring abatement therein are relatively low in concentration. This confluence of factors requires that significant capital and operating expenses be devoted to effluent and air-handling systems in the semiconductor manufacturing facility, as well as abatement equipment specific for the removal of the low-level contaminants of the effluent stream.
The cause of the high sweep exhaust requirement for ion implantation is twofold. The implantation process draws considerable energy from the numerous vacuum pumps employed, high temperature operation, the ion acceleration and separation equipment and the considerable electronics packages and power supplies create a large thermal heat load which must be removed. Today this heat is removed by sweeping large volumes of air through the interior space of the tool.
The ion precursor materials are typically gases and these are stored in a gas box inside the implanter. Standards mandate that the gas box be exhausted at a rate to dilute a worst case release to a concentration equal to xc2xc of the OSHA prescribed personal exposure level in the work space.
In ion implantation, a dopant species, such as Sb, In, B, As, P, etc., typically supplied by a source reagent, is contacted with an ion beam generator or ionizer to generate an icon beam. The resulting ion beam then is passed to a mass analyzer unit that selects the desired ions and rejects the non-selected ions.
The selected ions pass through an acceleration electrode array and deflection electrodes. A resultantly focused ion beam is impinged on a substrate element disposed on a rotatable holder mounted on a spindle in the ion implantation unit. The ion beam is used to dope the substrate as desired, to form a doped material for fabrication of the product microelectronic device structure.
Accordingly, a process effluent is produced from the ion implant chamber that is composed of various ionic fragments, reconstituted compounds, reaction byproducts, and included outgassed species from the ion implant chamber walls, in-leaking atmospheric gases which arc highly contaminated and in general only suited to be purified and vented. On a volumetric basis, this process effluent stream comprises about 1% of the total exhaust from the tool.
In sum, high exhaust gas flows have conventionally been encountered in the ion implantation field, where such high exhaust gas flows serve to dilute any toxic release emanating from a pump, piping or coupling malfunction as well as to remove latent heat from the large concentration of electrical equipment and pumps. As a consequence, conventional ion implanters are being exhausted at a flow rate of 2000 cubic feet per minute (CFM), in conventional practice. This high volumetric flow rate means that the exhaust-handling system must be oversized relative to the actual amount of hazardous material present in the effluent, and that larger capacity fans and blowers, etc. are required to accommodate the high flows, as well as larger and more expensive effluent treatment equipment. In addition replacement air must be re-supplied back to the manufacturing area. Typically this make-up air must be filtered, humidity adjusted and controlled to a set temperature.
A similar deficiency is present in wet bench systems commonly used in semiconductor manufacturing facilities. In the fabrication of semiconductor wafers, a multitude of aqueous cleaning steps are required to remove impurities from the surface of the wafer prior to subsequent processing. Generally, a batch of wafers is immersed into one or more chemical tanks (termed xe2x80x9cwet benchesxe2x80x9d) that contain chemicals that are needed for clean or etch functions.
Containment of hazardous chemicals in semiconductor wet processing systems is done today using below-deck exhaust systems, which function to capture chemical fumes or keep them at or below the deck. In order to effectively keep hazardous chemicals under control and out of the workspace above the deck, the below-deck exhaust systems have to effectuate flow of large volumes of filtered air through the wet cleaning tools at very high rates, e.g., on the order of 150 cubic feet per minute (cfm) per linear foot of the tool. High capacity exhaust systems are expensive, energy-consuming, and costly to install and maintain.
In wet benches it is typical to sweep large volumes of air through the mechanical areas of the bench (the area that contains the circulation pumps, chemical dispense and mixing). This is pre-cautionary and done largely to insure that small liquid leaks don""t lead to accumulations of hazardous and or corrosive materials in this area.
It therefore is apparent that there exist semiconductor processing operations that rely on bulk flows of xe2x80x9ccarrierxe2x80x9d or xe2x80x9csweepxe2x80x9d gas and that in consequence entail severe disadvantages in respect of capital and operating expenses in the semiconductor manufacturing facility. It would correspondingly be a significant advance in the semiconductor art to at least partially overcome such deficiencies of such prior art bulk gas flow processes.
The present invention relates to a system and process for reducing infrastructural requirements and operating costs of the aforementioned bulk gas flow processes.
In one aspect, the present invention relates to a gas recirculating system for use in a process facility generating a low-level contamination in a local gaseous environment in said process facility, said gas recirculating system comprising local gas flow circuitry having coupled thereto a chemical filter including a material having chemisorptive affinity for the low-level contamination, wherein the local gas flow circuitry is arranged and constructed for coupling to the local gaseous environment and flow of gas from the local gaseous environment through the chemical filter for removal of low-level contamination therefrom and recirculation thereof to the process facility.
In another aspect, the invention relates to a process for reducing exhaust gas load on a house exhaust system in a process facility generating a low-level contamination in a local gaseous environment in said process facility, said process comprising providing a local gas flow circuitry having coupled thereto a chemical filter including a material having chemisorptive affinity for the low-level contamination, flowing gas including low-level contaminants from the local gaseous environment through the local flow circuitry and chemical filter for removal of low-level contamination from said gas, and recirculating gas purified of said low level contaminants from the local flow circuitry to the process facility.
Other aspects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.